scholarly journals Methane Emissions from Surface of Mangrove River on Hainan Island, China

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1126
Author(s):  
Ji Hu ◽  
Wei Guan ◽  
Huai Chen
Keyword(s):  
Atmospheric Pressure ◽  
Mangrove Forest ◽  
Emission Rate ◽  
Hainan Island ◽  
Methane Flux ◽  
Tropical Rivers ◽  
Atmospheric Methane ◽  
Ch4 Flux ◽  
Water Characteristics ◽  
Freshwater River

The surfaces of rivers are considered important sources of atmospheric methane (CH4), however research on this topic is still constrained, especially in freshwater rivers and with the consideration of spatial heterogeneity. Three regions (upper reaches, midstream and downstream) were selected to examine the CH4 fluxes from a freshwater river surface in a mangrove forest wetland from 2012 to 2013, using floating chambers. Results showed that the CH4 fluxes varied significantly among the three regions, with the lowest fluxes at downstream (0.50 ± 0.20 mg m−2 h−1), and highest at upper reaches (1.19 ± 0.36 mg m−2 h−1). The average emission rate at midstream was 0.95 ± 0.37 mg m−2 h−1. The methane flux also varied with seasons, with higher flux in rain-abundant seasons. On average, the CH4 flux in our research river was 0.88 ± 0.31 mg m−2 h−1, which was less than other tropical rivers. In addition, we found that the CH4 flux was significantly correlated with the water characteristics of temperature and atmospheric pressure. Thereby, this study quantified the methane emission from a freshwater river surface in a tropical mangrove forest, enriching the existing knowledge of river surface CH4 flux.

Captured metagenomics reveals high spatial variability in functional potential in CH4 producing and consuming microorganisms in a temperate Swedish peatland.

2021 ◽  
Author(s):  
Joel White ◽  
Lena Ström ◽  
Dag Ahrén ◽  
Janne Rinne ◽  
Veiko Lehsten
Keyword(s):  
Microbial Communities ◽  
Root Zone ◽  
Water Concentration ◽  
Methane Flux ◽  
Functional Genes ◽  
Molecular Technique ◽  
Atmospheric Methane ◽  
Functional Potential ◽  
Methane Budget ◽  
Methane Metabolism

<p>Microbial communities of methane producing methanogens and consuming methanotrophs play an important role for the earths atmospheric methane budget. Despite their global significance, the functional potential of these communities is poorly understood. To investigate this, we applied the molecular technique, captured metagenomics, to identify the variability in functional diversity of microorganisms involved in the metabolism of methane<sub></sub>in an environmentally controlled laboratory study. Nine plant-peat mesocosms dominated by the sedge Eriophorum vaginatum, with varying coverage, were collected from a temperate natural wetland is Sweden and subjected to a simulated growing season. Samples for analysis of captured metagenomes were taken from the top, bottom and root adjacent zone at the end of the experiment. In addition, over the simulated season, measured gas fluxes of carbon dioxide (CO<sub>2</sub>) and CH<sub>4</sub>, δ<sup>13</sup>C of emitted CH<sub>4</sub> and the pore water concentration of dissolved methane and low molecular weight organic acids were recorded. The functional genes resulting from the captured metagenomes had a higher Shannon α-diversity in the root zone when compared to the bottom and top. Sequences coding for methane metabolism were significantly more diverse in the root and bottom zones when compared to the top. However, the frequency of Acetyl-CoA decarbonylase and methane monooxygenase subunit A were significantly higher in the high emitting methane flux category when compared to the medium and low emitting mesocosms. We conclude that captured metagenomic analyses of functional genes provides a good measure of the functional potential methanogenic and methanotrophic microbial communities. This technique can be used to investigate how methanogens and methanotrophs function in peatlands and thus, contribute to the concentration of atmospheric methane.</p>

scholarly journals Multi-year effect of wetting on CH<sub>4</sub> flux at taiga–tundra boundary in northeastern Siberia deduced from stable isotope ratios of CH<sub>4</sub>

2019 ◽  
Vol 16 (3) ◽  
pp. 755-768 ◽  
Author(s):  
Ryo Shingubara ◽  
Atsuko Sugimoto ◽  
Jun Murase ◽  
Go Iwahana ◽  
Shunsuke Tei ◽  
...  
Keyword(s):  
Water Saturation ◽  
Methane Flux ◽  
Interannual Variations ◽  
Ch4 Emission ◽  
Ch4 Flux ◽  
Ch4 Production ◽  
Year Effect ◽  
Northeastern Siberia ◽  
Order Of Magnitude ◽  
Acetoclastic Methanogenesis

Abstract. The response of CH4 emission from natural wetlands due to meteorological conditions is important because of its strong greenhouse effect. To understand the relationship between CH4 flux and wetting, we observed interannual variations in chamber CH4 flux, as well as the concentration, δ13C, and δD of dissolved CH4 during the summer from 2009 to 2013 at the taiga–tundra boundary in the vicinity of Chokurdakh (70∘37′ N, 147∘55′ E), located on the lowlands of the Indigirka River in northeastern Siberia. We also conducted soil incubation experiments to interpret δ13C and δD of dissolved CH4 and to investigate variations in CH4 production and oxidation processes. Methane flux showed large interannual variations in wet areas of sphagnum mosses and sedges (36–140 mg CH4 m−2 day−1 emitted). Increased CH4 emission was recorded in the summer of 2011 when a wetting event with extreme precipitation occurred. Although water level decreased from 2011 to 2013, CH4 emission remained relatively high in 2012, and increased further in 2013. Thaw depth became deeper from 2011 to 2013, which may partly explain the increase in CH4 emission. Moreover, dissolved CH4 concentration rose sharply by 1 order of magnitude from 2011 to 2012, and increased further from 2012 to 2013. Large variations in δ13C and δD of dissolved CH4 were observed in 2011, and smaller variations were seen in 2012 and 2013, suggesting both enhancement of CH4 production and less significance of CH4 oxidation relative to the larger pool of dissolved CH4. These multi-year effects of wetting on CH4 dynamics may have been caused by continued soil reduction across multiple years following the wetting. Delayed activation of acetoclastic methanogenesis following soil reduction could also have contributed to the enhancement of CH4 production. These processes suggest that duration of water saturation in the active layer can be important for predicting CH4 emission following a wetting event in the permafrost ecosystem.

scholarly journals Landscape analysis of soil methane flux across complex terrain

2018 ◽  
Vol 15 (10) ◽  
pp. 3143-3167 ◽  
Author(s):  
Kendra E. Kaiser ◽  
Brian L. McGlynn ◽  
John E. Dore
Keyword(s):  
Environmental Conditions ◽  
Methane Flux ◽  
Time Variability ◽  
Sink Strength ◽  
Watershed Scale ◽  
Ch4 Flux ◽  
Creek Watershed ◽  
Spatially Distributed ◽  
Dry Down ◽  
The Mean

Abstract. Relationships between methane (CH4) fluxes and environmental conditions have been extensively explored in saturated soils, while research has been less prevalent in aerated soils because of the relatively small magnitudes of CH4 fluxes that occur in dry soils. Our study builds on previous carbon cycle research at Tenderfoot Creek Experimental Forest, Montana, to identify how environmental conditions reflected by topographic metrics can be leveraged to estimate watershed scale CH4 fluxes from point scale measurements. Here, we measured soil CH4 concentrations and fluxes across a range of landscape positions (7 riparian, 25 upland), utilizing topographic and seasonal (29 May–12 September) gradients to examine the relationships between environmental variables, hydrologic dynamics, and CH4 emission and uptake. Riparian areas emitted small fluxes of CH4 throughout the study (median: 0.186 µg CH4–C m−2 h−1) and uplands increased in sink strength with dry-down of the watershed (median: −22.9 µg CH4–C m−2 h−1). Locations with volumetric water content (VWC) below 38 % were methane sinks, and uptake increased with decreasing VWC. Above 43 % VWC, net CH4 efflux occurred, and at intermediate VWC net fluxes were near zero. Riparian sites had near-neutral cumulative seasonal flux, and cumulative uptake of CH4 in the uplands was significantly related to topographic indices. These relationships were used to model the net seasonal CH4 flux of the upper Stringer Creek watershed (−1.75 kg CH4–C ha−1). This spatially distributed estimate was 111 % larger than that obtained by simply extrapolating the mean CH4 flux to the entire watershed area. Our results highlight the importance of quantifying the space–time variability of net CH4 fluxes as predicted by the frequency distribution of landscape positions when assessing watershed scale greenhouse gas balances.

scholarly journals Understanding Dynamics of Mangrove Forest on Protected Areas of Hainan Island, China: 30 Years of Evidence from Remote Sensing

2019 ◽  
Vol 11 (19) ◽  
pp. 5356 ◽  
Author(s):  
Liao ◽  
Zhen ◽  
Zhang ◽  
Metternicht
Keyword(s):  
Remote Sensing ◽  
Protected Areas ◽  
Mangrove Forest ◽  
Public Awareness ◽  
Hainan Island ◽  
Current Data ◽  
Support Vector ◽  
Mangrove Forests ◽  
Visual Interpretation ◽  
Wastewater Disposal

Implementation of the UN Sustainable Development Goals requires countries to determine targets for the protection, conservation, or restoration of coastal ecosystems such as mangrove forests by 2030. Satellite remote sensing provides historical and current data on the distribution and dynamics of mangrove forests, essential baseline data that are needed to design suitable policy interventions. In this study, Landsat time series were used to map trends and dynamics of mangrove change over a time span of 30 years (1987–2017) in protected areas of Hainan Island (China). A support vector machine algorithm was combined with visual interpretation of imagery and result showed alternating periods of expansion and loss of mangrove forest at seven selected sites on Hainan Island. Over this period, there was a net decrease in mangrove area of 9.3%, with anthropic activities such as land conversion for aquaculture, wastewater disposal and discharge, and tourism development appearing to be the likely drivers of this decline in cover. Long-term studies examining trends in land use cover change coupled with assessments of drivers of loss or gain enable the development of evidence based on policy and legislation. This forms the basis of financing of natural reserves of management and institutional capacity building, and facilitates public awareness and participation, including co-management.

scholarly journals Enrichment in <sup>13</sup>C of atmospheric CH<sub>4</sub> during the Younger Dryas termination

2011 ◽  
Vol 7 (5) ◽  
pp. 3287-3324 ◽  
Author(s):  
J. R. Melton ◽  
H. Schaefer ◽  
M. J. Whiticar
Keyword(s):  
Mass Balance ◽  
Gas Hydrates ◽  
Stable Carbon Isotope ◽  
Younger Dryas ◽  
Analytical Techniques ◽  
Carbon Isotope Ratio ◽  
Methane Flux ◽  
Atmospheric Methane ◽  
Stable Carbon ◽  
Thermokarst Lakes

Abstract. The abrupt warming across the Younger Dryas termination (~11 600 yr before present) was marked by a large increase in the global atmospheric methane mixing ratio. The debate over sources responsible for the rise in methane centers on the roles of global wetlands, marine gas hydrates, and thermokarst lakes. We present a new, higher-precision methane stable carbon isotope ratio (δ13CH4) dataset from ice sampled at Påkitsoq, Greenland that shows distinct 13C-enrichment associated with this rise. We investigate the validity of this finding in face of known anomalous methane concentrations that occur at Påkitsoq. Comparison with previously published datasets to determine the robustness of our results indicates a similar trend in ice from both an Antarctic ice core and previously published Påktisoq data measured using four different extraction and analytical techniques. The δ13CH4 trend suggests that 13C-enriched CH4 sources played an important role in the concentration increase. In a first attempt at quantifying the various contributions from our data, we apply a methane triple mass balance of stable carbon and hydrogen isotope ratios and radiocarbon. The mass balance results suggest biomass burning (42–66% of total methane flux increase) and thermokarst lakes (27–59%) as the dominant contributing sources. Our results do not suggest as large a role for tropical wetlands, boreal peatlands or marine gas hydrates as commonly proposed.

scholarly journals A model of the methane cycle, permafrost, and hydrology of the Siberian continental margin

2014 ◽  
Vol 11 (6) ◽  
pp. 7853-7900
Author(s):  
D. Archer
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Continental Margin ◽  
Methane Flux ◽  
Soil Freezing ◽  
Sediment Surface ◽  
Atmospheric Methane ◽  
Pore Waters ◽  
Methane Cycle ◽  
The Impact

Abstract. A two-dimensional model of a passive continental margin was adapted to the simulation of the methane cycle on Siberian continental shelf and slope, attempting to account for the impacts of glacial/interglacial cycles in sea level, alternately exposing the continental shelf to freezing conditions with deep permafrost formation during glacial times, and immersion in the ocean in interglacial times. The model is used to gauge the impact of the glacial cycles, and potential anthropogenic warming in the deep future, on the atmospheric methane emission flux, and the sensitivities of that flux to processes such as permafrost formation and terrestrial organic carbon (Yedoma) deposition. Hydrological forcing drives a freshening and ventilation of pore waters in areas exposed to the atmosphere, which is not quickly reversed by invasion of seawater upon submergence, since there is no analogous saltwater pump. This hydrological pump changes the salinity enough to affect the stability of permafrost and methane hydrates on the shelf. Permafrost formation inhibits bubble transport through the sediment column, by construction in the model. The impact of permafrost on the methane budget is to replace the bubble flux by offshore groundwater flow containing dissolved methane, rather than accumulating methane for catastrophic release when the permafrost seal fails during warming. By far the largest impact of the glacial/interglacial cycles on the atmospheric methane flux is attenuation by dissolution of bubbles in the ocean when sea level is high. Methane emissions are highest during the regression (soil freezing) part of the cycle, rather than during transgression (thawing). The model-predicted methane flux to the atmosphere in response to a warming climate is small, relative to the global methane production rate, because of the ongoing flooding of the continental shelf. A slight increase due to warming could be completely counteracted by sea level rise on geologic time scales, decreasing the efficiency of bubble transit through the water column. The methane cycle on the shelf responds to climate change on a long time constant of thousands of years, because hydrate is excluded thermodynamically from the permafrost zone by water limitation, leaving the hydrate stability zone at least 300 m below the sediment surface.

scholarly journals Topography-based modelling reveals high spatial variability and seasonal emission patches in forest floor methane flux

2020 ◽  
Author(s):  
Elisa Vainio ◽  
Olli Peltola ◽  
Ville Kasurinen ◽  
Antti-Jussi Kieloaho ◽  
Eeva-Stiina Tuittila ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Spatial Variability ◽  
Boreal Forest ◽  
Forest Floor ◽  
Methane Flux ◽  
Early Summer ◽  
Ground Vegetation ◽  
Small Scale ◽  
Ch4 Flux ◽  
Ch4 Uptake

Abstract. Boreal forest soils are globally an important sink for methane (CH4), while these soils are also capable to emit CH4 under favourable conditions. Soil wetness is a well-known driver of CH4 flux, and the wetness can be estimated with several terrain indices developed for the purpose. The aim of this study was to quantify the spatial variability of the forest floor CH4 flux with a topography-based upscaling method connecting the flux with its driving factors. We conducted spatially extensive forest floor CH4 flux and soil moisture measurements, complemented with ground vegetation classification, in a boreal pine forest. We then modelled the soil moisture with a Random Forest model using topography, based on which we upscaled the forest floor CH4 flux – this was performed for two seasons: May–July and August–October. Our results demonstrate high spatial heterogeneity in the forest floor CH4 flux, resulting from the soil moisture variability, as well as on the related ground vegetation. The spatial variability in the soil moisture and consequently in the CH4 flux was higher in the early summer compared to the autumn period, and overall the CH4 uptake rate was higher in autumn compared to early summer. In the early summer there were patches emitting high amounts of CH4, however, these wet patches got drier and smaller in size towards the autumn, which was enough for changing their dynamics to CH4 uptake. The results highlight the small-scale spatial variability of the boreal forest floor CH4 flux, and the importance of soil chamber placement in order to obtain spatially representative CH4 flux results. We recommend that a site of similar size and topographical variation would require 15–20 sample points in order to achieve accurate forest floor CH4 flux.

scholarly journals An analysis of atmospheric CH<sub>4</sub> concentrations from 1984 to 2008 with a single box atmospheric chemistry model

2012 ◽  
Vol 12 (11) ◽  
pp. 30259-30282 ◽  
Author(s):  
Z. Tan ◽  
Q. Zhuang
Keyword(s):  
Growth Rate ◽  
Atmospheric Chemistry ◽  
Methane Flux ◽  
Methane Emissions ◽  
Atmospheric Methane ◽  
Significant Drop ◽  
Oxidizing Power ◽  
The Mean

Abstract. We present a single box atmospheric chemistry model involving atmospheric methane (CH4), carbon monoxide (CO) and radical hydroxyl (OH) to analyze atmospheric CH4 concentrations from 1984 to 2008. When OH is allowed to vary, the modeled CH4 is 20 ppb higher than observations from the NOAA/ESRL and AGAGE networks for the end of 2008. However, when the OH concentration is held constant at 106 molecule cm−3, the simulated CH4 shows a trend approximately equal to observations. Both simulations show a clear slowdown in the CH4 growth rate during recent decades, from about 13 ppb yr−1 in 1984 to less than 5 ppb yr−1 in 2003. Furthermore, if the constant OH assumption is credible, we think that this slowdown is mainly due to a pause in the growth of wetland methane emissions. In simulations run for the Northern and Southern Hemispheres separately, we find that the Northern Hemisphere is more sensitive to wetland emissions, whereas the southern tends to be more perturbed by CH4 transportation, dramatic OH change, and biomass burning. When measured CO values from NOAA/ESRL are used to drive the model, changes in the CH4 growth rate become more consistent with observations, but the long-term increase in CH4 is underestimated. This shows that CO is a good indicator of short-term variations in oxidizing power in the atmosphere. The simulation results also indicate the significant drop in OH concentrations in 1998 (about 5% lower than the previous year) was probably due to an abrupt increase in wetland methane emissions during an intense EI Niño event. Using a fixed-lag Kalman smoother, we estimate the mean wetland methane flux is about 128 Tg yr−1 through the period 1984–2008. This study demonstrates the effectiveness in examining the role of OH and CO in affecting CH4.

scholarly journals Seasonal and spatial variability of methane emissions from a subtropical reservoir in Eastern China

2018 ◽  
Author(s):  
Le Yang ◽  
Hepeng Li ◽  
Chunlei Yue ◽  
Jun Wang
Keyword(s):  
Spatial Variability ◽  
Time Scales ◽  
Seasonal Variability ◽  
Eastern China ◽  
Methane Emissions ◽  
Spatiotemporal Variability ◽  
Ch4 Emission ◽  
Atmospheric Methane ◽  
Ch4 Flux ◽  
Minimum Value

Abstract. Subtropical reservoirs are important source of atmospheric methane (CH4). This study aims to investigate the spatiotemporal variability of CH4 emission, using the methods of static floating chambers and bubble traps, from the water surfaces of Xin'anjiang Reservoir. Seasonal variability showed that CH4 emission from the main reservoir body was high in autumn and low in spring, with medium values in summer and winter. The dynamics of CH4 emission was flat from February to June, but fluctuated dramatically from July to January in the upstream river, which was interrupted by the bubbles in the second half year. However, CH4 emission was largely influenced by the streamflow in the downstream river, with a minimum value in February due to an extreme low streamflow (275 m3 s−1). Spatial variability showed the upstream river had the highest CH4 flux (3.90 ± 7.80 mg CH4 m−2 h−1), followed by the downstream river (0.50 ± 0.41 mg CH4 m−2 h−1), and the main reservoir body stood the last place (0.01 ± 0.07 mg CH4 m−2 h−1). Therefore, it was necessary to capture the variation of CH4 emission from reservoirs in the space and time scales to avoid the error of estimating the CH4 emission incorrectly.

scholarly journals Community Structure and Biodiversity of Soil Ciliates at Dongzhaigang Mangrove Forest in Hainan Island, China

2010 ◽  
Vol 2010 ◽  
pp. 1-8 ◽  
Author(s):  
Jing Li ◽  
Qingyu Liao ◽  
Mei Li ◽  
Jinhong Zhang ◽  
Nora Fungyee Tam ◽  
...  
Keyword(s):  
Organic Matter ◽  
Community Structure ◽  
Mangrove Forest ◽  
Chemical Properties ◽  
Hainan Island ◽  
Community Similarity ◽  
Dominant Group ◽  
Soil Ciliates ◽  
Physical Chemical ◽  
Total Potassium

The distribution of soil ciliates in three different habitats within a typical mangrove forest in Dongzhaigang, Hainan, China was investigated. The abundance, biodiversity, and community similarity of ciliates in fresh and air-dried soil with different, physical/chemical properties were analyzed. Three Classes, 11 Orders, 34 Genera, and 70 species of ciliates were found with the first dominant group being Hypotrichida. Ciliate biodiversities followed Site B < Site A < Site C in both fresh and dried samples. Ciliate abundance was positively correlated with soil moisture, salinity, organic matter (OM), total nitrogen (TN), total phosphorus (TP), and sulfate (SO42−), but negatively with pH and total potassium (TK). Site A and Site B and Site B and Site C showed the highest similarity in fresh and dried samples, respectively. The ubiquitous characteristics of ciliate distribution suggested their important role in food webs and nutrient cycling. The presence of Colpodida was linked with mangrove plants.

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